A Paradox of Sustainability

When discussing Malthus, I said that we don’t need to worry about “overpopulation”, because there are no global food shortages in the foreseeable future. A natural response to this is that we may be able to feed more people, but they would consume other resources and pollute in an unsustainable fashion. I have previously expressed several reservations about the idea of sustainability, and I stand by those. Most environmental problems are not necessary results of overpopulation or a high discount rate that undervalues future generations. I cannot think of an environmental problem that is not caused by externalities or a lack of property rights, and thus could not be solved by the proper application of Pigouvian taxes or property rights. Many of these solutions would work fast enough to be worth it to current people at current discount rates; we should have higher gas taxes and property rights in fish regardless of “sustainability”.

Of course, even with these fixes, there will still be increasing amounts of some pollution. Part of this is due to discounting the future, which could be reduced in an non-distortionary way by lowering taxes on saving and investment. Even at a zero discount rate, though, we may still leave the world more polluted than we found it, for instance with more carbon dioxide. Would this be “unsustainable”?

One definition of sustainability is “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. In economics terms, this means we should have no time rate of preference (we should care about the future as much as the present); in Rawlsian terms, we should arrange society as we would if we didn’t know which generation we would be born in. I have previously argued that high pollution and consumption can be sustainable because future generations will probably be richer and we aren’t sure how much they will value our actions. In finance terms, this is like taking out loans instead of saving because you think your income will be higher in the future and because investments are risky. Such an individual would take out loans even if they value their present and future selves equally.

All of these criticisms simply reduce the scope of sustainability; but it is still reasonable to reduce some pollution and consumption if you think future generations will be poorer than us and you have a good idea of what they will value (though I think they will be much richer than us). The actual contradiction comes when we consider “overpopulation”. It is often said that people today should have fewer kids because a higher population is not “sustainable”. If we have fewer kids, there will be more resources per person; each person in the future will be able to pollute and consume more. How is this a problem?

Robert Solow pointed out one contradiction of sustainability (though he was kind enough to call it a “paradox”) when he said (page 7, it is worth reading all 9):

“I want to mention what strikes me as a sort of paradox- as a difficulty with a concept of sustainability. I said, I kind of insisted, that you should think about it as a matter of equity…. how productive capacity should be shared between us and them, them being the future. Once you think about it that way you are almost forced logically to think about not between periods of time but equity right now…. the paradox arises because if you are concerned about people who are currently poor, it will turn out that your concern for them will translate to an increase in [current] consumption”

This is one contradiction, that we want equity across generations, and we achieve it by worsening current inequality. We tell poor Brazilians not to clear land for their farms, poor Chinese not to burn coal to light their homes, poor Africans not to use DDT to protect their health; all so people in the future can enjoy more species and a stable climate. This seems to be a transfer from poor to rich in the name of equity. But Solow, right after pointing out one contradiction, stumbles into another, saying “control of population growth would probably be the best available policy on behalf of sustainability”.

This creates another kind of inequality. Say a future generation can safely consume and pollute 10 units, spreading this over 10 people, so each person gets one unit of “exhaustible GDP”. Are we being equitable if instead we control population so that there are only 5 people and they can each have 2 units of goods? No, we are making the rich (who get to experience life) richer with an extra good per person, while the 5 “poor” don’t get to exist at all or consume anything.

Further, the only ways to explain away the problem are blocked by the logic of sustainability itself. One could say that the people who don’t exist shouldn’t be counted; but the whole point of sustainability is to speak up for future generations who don’t yet exist and so can’t speak for themselves. One could say that a life that is allowed little pollution or consumption of exhaustible resources is not worth living; but the whole strategy of sustainability is to tell people that life is still good when you pollute little, consume little, and draw enjoyment from things besides consumerism and materialism.

So an argument that we should have fewer kids to be sustainable and equitable is really an argument for increasing inequality in the future. It does not make sense on equity grounds; sustainability needs to drop the idea of population control to be logically consistent (except insofar as it does prevent famine and musicals). The new growth theory and a host of empirical work have also established that it doesn’t make sense on efficiency grounds, since the externality of a marginal child ispositive.

There are lots of good reasons not to have kids, but a worry about sustainability is not one of them.